Heat Release Pattern Research Articles

Control of combustion process in an HCCI-DI combustion engine using dual injection strategy with EGR

The objective of this study was to achieve a controlled HCCI-DI combustion using in-cylinder dual injection technique and to study the effect of premixed ratio and EGR on combustion, performance and emission characteristics of the engine. Studies were carried out up to 67% (0–67%) of the full load and a constant speed of 1500rev/min. The premixed ratio was varied from zero to a maximum of 80% of the total fuel by mass. At 50% load condition, occurrences of peak pressure, peak PRR and peak HRR varied within 5–7deg BTDC, 1.5–5deg BTDC and 1–4deg BTDC respectively. It was observed that diesel homogeneous combustion showed a two phase heat release pattern at higher premixed ratios and all combustion parameters advanced dramatically with increasing premixed ratio. The results showed that a reduction of 76% in NOX and 40% in smoke opacity were achieved using 80% premixed ratio with 30% EGR. As the premixed ratio was increased, there was an improvement in IMEP, ISFC and smoke opacity with penalties in HC and CO emissions.

Investigation on the flame characteristics in a PCCI engine using endoscope system with micro-cassegrain

Diesel engines are most frequently used in vehicles because of their high efficiency and durability. However, nitrogen oxide (NOx) and particulate matter (PM) from diesel engines are became problem. Recently, the premixed charged compression ignition (PCCI) technique has been studied specifically to reduce NOx and PM emissions simultaneously. While the PCCI engine has the advantage of reducing NOx and PM emissions, control of the combustion phase is difficult. Therefore, it is very important to understand the flame developing process and heat release pattern in a real PCCI engine. However, most research into the characteristics of PCCI combustion has used an optical access engine. This paper describes the combustion characteristics obtained using a micro-Cassegrain sensor and discusses how the sensor can be used to directly detect the flame characteristics for future control of PCCI combustion. From this research, the differences of flame characteristics between PCCI engine and conventional diesel engine were clarified.

Studies on the effect of hydrogen induction on performance, emission and combustion behaviour of a WCO emulsion based dual fuel engine

This paper aims at studying the effect of hydrogen induction on engine performance, emission and combustion behaviour of a diesel engine fuelled with the emulsion of used palm oil (called as WCO-waste cooking oil) as pilot fuel and hydrogen as primary fuel. A single cylinder water-cooled direct injection diesel engine was tested at 100% and 40% loads. Results were compared with neat diesel, neat WCO and WCO emulsion at both loads in single fuel operation. WCO emulsion in single fuel mode indicated improvement in performance and reduction in all emissions as compared to neat WCO. Dual fuel operation with hydrogen induction further reduced the emissions of smoke HC and CO with WCO as pilot fuel at all power outputs. However, hydrogen induction resulted in reduced thermal efficiency at 40% load. WCO emulsion showed higher ignition delay as compared to neat WCO. Dual fuel operation with hydrogen induction increased the ignition delay further. Heat release pattern showed higher premixed combustion rate with hydrogen induction mainly at high power outputs. Premixed combustion rate became very high at higher rates of hydrogen admission mainly at high power output. In general, hydrogen induction showed superior performance at high power output and inferior performance at low power output with WCO emulsion as injected fuel.

Investigation of the combustion and emission characteristics of partially premixed compression ignition in a heavy-duty diesel engine

Partially premixed compression ignition in a diesel engine is a combustion mode between diffusion combustion and homogeneous charge compression ignition combustion, the combustion controllability and the emission performances of which are close to those of a homogeneous charge compression ignition combustion engine; the mixing period plays a key role in realizing partially premixed compression ignition, and a long premixed process before combustion is necessary to make the fuel and air mix well. Partially premixed compression ignition combustion in a boosted six-cylinder heavy-duty diesel engine is realized by adjusting the injection timing and the rate of exhaust gas recirculation based on a single injection. The effects of the injection timing, the exhaust gas recirculation rate and the load rate on the combustion and the heat release pattern are studied. The factors which influence the mixing period and the ignition delay and its regularity are researched. Endoscope technology and the two-colour method are also used to gain an insight into partially premixed compression ignition combustion. The results show that both early injection and late injection have a long mixing period, which helps to form a more homogeneous mixture, and no diffusion combustion is found in the heat release rate curves. Premixed combustion and low-temperature combustion are the key factors in reducing the particulate matter emissions and nitrogen oxide emissions simultaneously. However, the low-temperature combustion and the dilute mixture may lead to incomplete combustion; consequently, for relatively late-injection conditions, the hydrocarbon and carbon monoxide emissions increase dramatically and the fuel consumption becomes worse. In these partially premixed combustion patterns, the effect of the injection pressure on the particulate matter and nitrogen oxide emissions is not clearly observable. At lower load rates, partially premixed compression ignition combustion displays a low-temperature and a high-temperature two-stage heat release. When the engine load rate is increased to 50%, diffusion combustion appears in the early-injection modes, which leads to higher nitrogen oxide and particulate matter emissions.

Studies on potential utilization of rice husk char in blend with lignite for cocombustion application

Combustion behavior of Indian lignite sample blended with rice husk chars (prepared at low temperature) has been examined in this study through simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) technique. Range of inputs obtainable by characteristic TG–DSC parameters has been utilized to arrive at important conclusions and observations in respect of ideal selection of blend proportion, proper utilization of the blend combination, etc. Deviations of experimental mass loss pattern (TG) and of rate curve (DTG) from corresponding expected theoretically calculated pattern have also been noted for different blends to examine possible advantageous or disadvantageous effects. As per the observations recorded, use of biomass char in blends (with lignite) was found to be very much beneficial and its proportion in the blends may be restricted to a level of 40 % by mass to extract maximum benefits in burning performance. This paper also focuses specific advantages of use of rice husk char in place of raw rice husk for cocombustion applications. Moreover, the importance of heat release pattern to assess compatibility of a fuel mix with existing boiler design and also to workout fresh boiler design for cocombustion application has been discussed in this paper.

대형기관 모사 정적연소실에서 매립지 가스의 연소특성에 대한 연구 (II) - 연소 분석 -

This is the second paper on the combustion characteristics of landfill gas in a constant volume combustion chamber for a large displacement volume commercial engine, and it discusses the combustion process on the basis of pressure measurements. The results show that the bimodal peak pressure phenomenon, which is caused by the interaction of the heat release and the heat transfer, is more apparent as the mixtures are more favorable to combustion, and the magnitudes of the pressures depend on the unburned fraction. In addition, there exist four main inflection points during heat release owing to variations in the heat transfer area related to flame propagation from the ignition point. Furthermore, the number of inflection points increases as the mixture quality worsens because of the extended burn duration. Consequently, the sophisticated interactions between the heat transfer area changing pattern due to flame propagation and transfer duration might cause very peculiar heat release patterns.

Commercial Naphtha Blends for Partially Premixed Combustion

Partially Premixed Combustion has shown the potential of low emissions of nitrogen oxides (NOx) and soot with a simultaneous improvement in fuel efficiency. Several research groups have shown that a load range from idle to full load is possible, when using low-octane-number refinery streams, in the gasoline boiling range. As such refinery streams are not expected to be commercially available on the short term, the use of naphtha blends that are commercially available could provide a practical solution. The three blends used in this investigation have been tested in a single-cylinder engine for their emission and efficiency performance. Besides a presentation of the sensitivity to injection strategies, dilution levels and fuel pressure, emission performance is compared to legislated emission levels. Conventional diesel combustion benchmarks are used for reference to show possible improvements in indicated efficiency. Analysis of the heat release patterns revealed an interesting and strong correlation between the premixed fraction and the amount of soot produced. To be specific, each of the fuels showed a decrease in this fraction as either fuel pressure was lowered or load was increased, showing a transition from more premixed to mainly mixing-controlled combustion, with the corresponding soot emissions. For one blend, over the whole load range EURO VI PM levels were approached or achieved, combined with a peak gross indicated efficiency of 50% clearly indicating the potential of this concept.

Effect of Transient Residual Gas Fraction for Gasoline Engines

The residual gas fraction (RGF) greatly affects misfiring, the heat release pattern of combustion, the NOx emission, knocking, the auto-ignition and the spark advance control. There is a possibility that a RGF estimation improves the accuracy of engine control. This paper describes a transient RGF estimation based on a physical model and the effect of RGF on combustion and transient air fuel ratio. This study shows the auto-correlation function takes negative values at k = 1 (k: engine cycle number) and the residual gas causes the dynamics of air-fuel ratio calculated from the composition of burned gas.

Experiments and zero D modeling studies using specific Wiebe coefficients for producer gas as fuel in spark-ignited engines

The paper addresses experiments and modeling studies on the use of producer gas, a bio-derived low energy content fuel in a spark-ignited engine. Producer gas, generated in situ, has thermo-physical properties different from those of fossil fuel(s). Experiments on naturally aspirated and turbo-charged engine operation and subsequent analysis of the cylinder pressure traces reveal significant differences in the heat release pattern within the cylinder compared with a typical fossil fuel. The heat release patterns for gasoline and producer gas compare well in the initial 50% but beyond this, producer gas combustion tends to be sluggish leading to an overall increase in the combustion duration. This is rather unexpected considering that producer gas with nearly 20% hydrogen has higher flame speeds than gasoline. The influence of hydrogen on the initial flame kernel development period and the combustion duration and hence on the overall heat release pattern is addressed. The significant deviations in the heat release profiles between conventional fuels and producer gas necessitates the estimation of producer gas-specific Wiebe coefficients. The experimental heat release profiles are used for estimating the Wiebe coefficients. Experimental evidence of lower fuel conversion efficiency based on the chemical and thermal analysis of the engine exhaust gas is used to arrive at the Wiebe coefficients. The efficiency factor a is found to be 2.4 while the shape factor m is estimated at 0.7 for 2% to 90% burn duration. The standard Wiebe coefficients for conventional fuels and fuel-specific coefficients for producer gas are used in a zero D model to predict the performance of a 6-cylinder gas engine under naturally aspirated and turbo-charged conditions. While simulation results with standard Wiebe coefficients result in excessive deviations from the experimental results, excellent match is observed when producer gas-specific coefficients are used. Predictions using the same coefficients on a 3-cylinder gas engine having different geometry and compression ratio(s) indicate close match with the experimental traces highlighting the versatility of the coefficients.

Effects of Damköhler number on vortex–flame interaction

Oscillating heat release associated with large-scale vortex structures in a dump combustor was investigated experimentally. The objectives were to understand vortex–heat release interactions that may lead to combustion instability and to characterize spatial patterns in fluctuating heat release for future control purposes. The inlet jet, which consisted of a turbulent premixed ethylene–air flow, was acoustically forced to control shedding of periodic vortices. The reacting flowfield was characterized using a phase-locked schlieren technique, while the corresponding heat release pattern was investigated using CH * chemiluminescence. Phase-resolved data taken at various flow conditions were compared to identify important physical parameters. In the context of vortex-driven combustion instability, the results showed that the Damköhler number was a critical parameter for vortex–heat release interaction. When the Damköhler number was relatively high, the leading edge of the vortices coincided with the high point in the local heat release cycle and the trailing edge with the low point. However, a clear shift in the heat release pattern was observed at Damköhler numbers lower than four. Under these conditions, the high point in local heat release was observed either in the vortex core or at the trailing edge of the vortex. Accordingly, the effect of the Damköhler number must be taken into consideration when designing an active control strategy based on secondary fuel injection.

Controlled three-stage heat release of stratified charge compression ignition (SCCI) combustion with a two-stage primary reference fuel supply

This paper discusses the heat release mode and its effect on combustion characteristics of stratified charge compression ignition (SCCI) combustion with a two-stage fuel supply. To create and control the fuel concentration stratification, composition stratification, and temperature stratification, primary reference fuels or their mixtures were supplied from the intake port, while n-heptane was directly injected into the cylinder near the top dead center of the compression stroke. To achieve a controllable staged heat release and to optimize the thermal efficiency and emissions, important factors, including premixed fuel properties, direct injection timing, the overall equivalence ratio, and the premixed ratio were tuned to modulate the heat release pattern. The experimental results revealed that, with the port fuel injection of a two-stage reaction fuel, the heat release curve of the SCCI combustion exhibits a three-stage heat release pattern. The in-cylinder fuel delivery advance angle plays an important role in the indicated thermal efficiency, and the earlier fuel delivery angle has a positive effect on the indicated thermal efficiency. It should be noted that an excessively advanced fuel delivery angle will lead to a sharp increase of NOx emissions. With the port fuel injection of PRF50, both fuel efficiency and ultra-low NOx emissions were obtained over wide ranges of the premixed ratio and the equivalence ratio. Moreover, the experimental results suggest that a higher premixed ratio for low-to-medium equivalence ratios and a smaller premixed ratio for larger equivalence ratios are preferred. The maximum thermal efficiency was observed at the zone with the earlier CA50 but with shorter burn duration. NOx levels were determined not only by CA50 and burn duration but also by the heat release mode. One-stage SCCI combustion, which was dominated by the diffusion burn, exhausted considerable NOx emissions, compared to the staged heat release mode.

Performance analysis of 1,4 dioxane-ethanol-diesel blends on diesel engines with and without thermal barrier coating

1,4 dioxane, a new additive allows the splash blending of ethanol in diesel in a clear solution. The objective of this investigation is to first create a stable ethanol-diesel blended fuel with 10% 1,4 dioxane additive, and then to generate performance, combustion and emissions data for evaluation of different ethanol content on a single cylinder diesel engine with and without thermal barrier coating. Results show improved performance with blends compared to neat fuel for all conditions of the engine. Drastic reduction in smoke density is found with the blends as compared to neat diesel and the reduction is still better for coated engine. NOx emissions were found to be high for coated engines than the normal engine for the blends. The oxygen enriched fuel increases the peak pressure and rate of pressure rise with increase in ethanol ratio and is still superior for coated engine. Heat release pattern shows higher premixed combustion rate with the blends. Longer ignition delay and shorter combustion duration are found with all blends than neat diesel fuel.

Heat Release Pattern Diagnostics to Improve Diesel Low Temperature Combustion

Heat Release Pattern Diagnostics to Improve Diesel Low Temperature Combustion

Effects of injection angles on combustion processes using multiple injection strategies in an HSDI diesel engine

Effects of injection angles and injection pressure on the combustion processes employing multiple injection strategies in a high-speed direct-injection (HSDI) diesel engine are presented in this work. Whole-cycle combustion and liquid spray evolution processes were visualized using a high-speed video camera. NO x emissions were measured in the exhaust pipe. Different heat release patterns are seen for two different injectors with a 70-degree tip and a 150-degree tip. No evidence of fuel-wall impingement is found for the first injection of the 150-degree tip, but for the 70-degree tip, some fuel impinges on the bowl wall and a fuel film is formed. For the second injection, a large amount of fuel deposition is observed for the 70-degree tip. Weak flame is seen for the first injection of the 150-degree tip while two sorts of flames are seen for the first injection of the 70-degree tip including an early weak flame and a late luminous film combustion flame. Ignition occurs near the spray tip in the vicinity of the bowl wall for the second injection events of the 150-degree tip, however, it is near the injector tip in the central region of the bowl for the 70-degree tip. The flame is more homogeneous for the 150-degree tip with higher injection pressure with little soot formation similar to a premixed-charge-compression-ignition (PCCI) combustion. For other cases, liquid fuel is injected into flames showing diffusion flame combustion. More soot luminosity is seen for the 70-degree tip due to significant fuel film deposition on the piston wall with fuel film combustion for both injection events. Lower NO x emissions were obtained for the narrow-angle injector due to the rich air–fuel mixture near the bowl wall during the combustion process. Increasing injection pressure leads to increased NO x emissions for both injection angles because of the relatively leaner and faster combustion process with higher in-cylinder temperature for the increased injection pressure.

Fast heat release characterization of a diesel engine

Multi-event fuel injection strategies under independently controlled exhaust gas recirculation and intake boost have been applied to produce the heat release patterns that characterize the clean combustion techniques of modern diesel engines. Extensive experimental and analytical comparisons have been performed to better estimate the heat release characteristics from the cylinder pressure traces. A number of heat release models based on the First Principles are compared against a comprehensive heat release model, on the basis of numerical complexity and the ability to characterize the combustion process. Such study indicated that though the estimation from the simplified models is efficient when the heat release is close to the end of the cylinder compression stroke, the simplified models produce shortfalls in estimating the more spread multi-event heat release from the newer combustion systems. A new computationally efficient algorithm, based on the Diesel Pressure Departure Ratio, is proposed to characterize the various heat release patterns with adequate accuracy. The improved heat release analyzing algorithms are further programmed on real-time deterministic devices that process the cylinder pressure data to provide the necessary feedback for the fuel-injection model running on subsequent real-time controllers. The efficacy of the new algorithms has been experimentally demonstrated against selected cases of boost, engine load and exhaust gas recirculation on a modern diesel engine.

Effect of design parameters on performance of a top fired natural gas reformer

A three-dimensional zone method was applied to an industrial fired heater of methane steam reforming reactor. Radiation heat transfer from all gases and surfaces inside the furnace was considered. Results from previous work and data of an industrial top fired furnace were used to validate the model. A maximum temperature in external reaction tube skin was obtained at about one third of the reactor length from top in the industrial furnace. Effect of important parameters such as emissivity, extinction coefficient, heat release pattern and flame angle on performance of the fired heater are presented. It was found that decreasing the extinction coefficients of combustion gases by 25% (from about 0.20 to 0.15) caused 2.6% rise in temperature of heat sink surfaces. It was demonstrated that the three-dimensional zone method developed in this work is simple, easy and flexible for modeling and simulation of the fired heaters.

Ethanol animal fat emulsions as a diesel engine fuel – Part 2: Engine test analysis

This work aims on the efficient use of animal fat in a diesel engine by making its stable emulsions with ethanol and water. A single cylinder direct injection diesel engine is tested using neat diesel, neat animal fat and animal fat emulsion (optimal emulsion) as fuels under variable load operating conditions. Results show increased peak pressure and ignition delay with ethanol animal fat emulsion as compared to neat fat. Heat release pattern shows improvement in the premixed combustion phase with animal fat emulsion as compared to neat animal fat. Drastic reduction in smoke, nitric oxide, hydrocarbon and carbon monoxide emissions are observed with the emulsion as compared to neat fat and neat diesel mainly at high power outputs. Only, hydrocarbon and carbon monoxide emissions are found as high with the emulsion at light loads. In general, animal fat emulsion shows considerable reduction in all emissions and improvement in engine performance as compared to neat fat.

Effect of water and methanol fractions on the performance of a CI engine using animal fat emulsions as fuel

The influence of water and methanol (W/M) fractions on the performance of a compression ignition engine fuelled with animal fat (obtained from duck) emulsions is studied. A single cylinder air-cooled, direct injection diesel engine developing a rated brake power output of 2.8 kW at 1500 r/min is tested using diesel neat animal fat, and animal fat emulsions with different fractions of W/M. Results show reduced peak pressure with neat animal fat when compared with diesel. Animal fat emulsions result in increased peak pressure with increased W/M fractions. Ignition delay is quite high with neat animal fat. Increase in W/M amounts in the emulsions further increase the ignition delay. Heat release pattern shows improved combustion rates with animal fat emulsions at all W/M fractions when compared with neat animal fat. Drastic reduction in smoke emission from 3.6 m−1 with neat animal fat to a minimum of 0.5 m−1 is achieved with the animal fat emulsion at the maximum W/M fraction. NO emission is found to be lower with neat animal fat than with neat diesel. Animal fat emulsions further reduce NO emission at all W/M fractions. Hydrocarbon and carbon monoxide emissions are also reduced significantly with animal fat emulsions at all W/M ratios when compared with neat animal fat. In general, animal fat emulsions with different W/M fractions show considerable reduction in all emissions and improvement in engine performance when compared with neat animal fat. Emulsion of 10W10M2S83 (i.e. 10 per cent of water, 10 per cent of methanol, and 2 per cent of span 83 by volume) is found to be the best among the three tested emulsions for optimum performance and emissions.

Experimental investigations on the use of preheated animal fat as fuel in a compression ignition engine

The effect of fuel inlet temperature on performance, emission and combustion characteristics of a diesel engine is evaluated. A single cylinder direct injection diesel engine developing a power output of 2.8 kW at 1500 rev/min is tested using preheated animal fat as fuel. Experiments are conducted at the fuel inlet temperatures of 30, 40, 50, 60 and 70 °C. Animal fat at low temperature results in higher ignition delay and combustion duration than diesel. Preheated animal fat shows reduced ignition delay and combustion duration. Peak pressure and rate of pressure rise are found as high with animal fat at high fuel inlet temperatures. Heat release pattern shows reduced premixed combustion phase with animal fat as compared to neat diesel at normal temperature. Preheating improves the premixed combustion rate. At low temperature, animal fat results in lower smoke emissions than diesel. The maximum smoke density is K=6.5 m −1 with diesel and K=3.6 m −1 with animal fat at 30 °C. Preheated animal fat further reduces smoke levels at all temperatures. The smoke level is reduced up to K=1.7 m −1 with preheated animal fat at the temperature of 70 °C. Hydrocarbon and carbon monoxide emissions are higher with animal fat at low temperature as compared to diesel. Fuel Preheating reduces these emissions. NO emission is found as low with animal fat at low temperature. Fuel preheating results in increased NO emission. However, the level is still lower than diesel even at high temperature (i.e. 70 °C). On the whole it is concluded that preheated animal fat can be used in diesel engines with reduced smoke, hydrocarbon and carbon monoxide emissions with no major detoriation in engine performance.

Instability Mechanisms in a Premixed Prevaporized Combustor

Instabilities in a premixed prevaporized 150-kW model scale combustor are investigated experimentally. The injector fed with liquid heptane and preheated air features two sets of swirling blades that induce flow rotation in the same direction (corotative) or in the opposite direction (counter-rotative). The flame is stabilized with swirl behind a dump. Instabilities occur in the low-frequency range around 400 Hz corresponding to a quarter-wave mode acoustic coupling of the system. Simultaneous measurements of pressure and heat-release oscillations and phase-locked CH chemiluminescence images are used to characterize the combustion dynamics. In both corotative (COS) and counter-rotative (CNS) cases, the reaction region moves closer to the injector when the flame becomes unstable by about one-third of the stabilization distance under normal operation. Experiments indicate that the two swirl configurations have distinct domains of instability. The instability boundary separating stable and unstable regions can be defined in terms of a critical velocity v c , which depends on the equivalence ratio Φ, air injection temperature T i n j , and swirl geometry. In the coswirl configuration, instabilities occur when the injection velocity is lower than the critical velocity [u v c (Φ, T i n j ; CNS)]. In a range of conditions corresponding to low injection velocities, reduced eqivalence ratio, and for the coswirl configuration, an unsteady flashback takes place in which the flame moves periodically in and out of the fuel premixer. This mechanism is related to the existence of a low-velocity region near the injector exit plane. Observations of the space-time development of the heat release under unstable operation indicate that the oscillations are significantly influenced by the swirl geometry and are caused by different mechanisms. The coswirl configuration features a central recirculation, which gives rise to periodic vortex roll-up, convection, and sudden release of heat when the vortices impinge on the lateral walls. In the counterswirl geometry there are no identifiable flow structure, but the heat-release pattern is convected periodically in the chamber. Estimates of the delay times associated with the two mechanisms support the view that coswirl instabilities are driven by vortex roll-up, whereas counterswirl instabilities are probably sustained by equivalence-ratio inhomogeneities.